There are three 10 ohm resistors connected in series.
The equivalent resistance of two 10 ohm resistors is 10 ohm + 10 ohm = 20 ohm. The first measurement error is 0.5%, while the second one shows the exact expected value.
The equivalent resistance of three ohm resistors is 10 ohm + 10 ohm + 10 ohm = 30 ohm. The measured resistance of these three resistors is 29.8 ohm; the percent error 0.67%
